This invention relates generally to devices and systems for measuring concentrations of ions, chemicals, biological materials, and reaction products, and more particularly, to a solid state device which employs a silicone rubber matrix, having electrochemical properties comparable in quality to conventional PVC membranes, as the substance-sensitive membrane, and wherein the silicone rubber membrane exhibits excellent adhesion to the Si.sub.3 N.sub.4 surface of solid state sensors.
As a result of their small size and potentially lower cost, solid state ion sensors are of interest in industrial and medical applications as replacements for traditional ion-selective electrodes. These sensors make possible new direct-monitoring applications. There is a need, however, for improved membrane adhesion, as such would be beneficial, not only to all users of solid-state chemical sensors, but particularly those interested in long-term monitoring.
Basically, the potential uses of solid-state ion sensors can be divided into industrial and medical applications. Industrial uses include, for example, the monitoring of treated or waste water for hardness or pollutants; on-line analysis of industrial chemicals, foodstuffs, and medicines; and low cost analytical instruments. Medical applications include the monitoring of electrolytes, blood gases, and metabolic substrates, both for biochemical control systems and for patient monitoring or diagnostics. There is a need for solid state ion sensors which can achieve the needs of industrial and medical monitoring for very long periods of time. Silicone-based chemical sensors often use ionophore-doped polymeric membranes as transducers because of their excellent selectivity toward the ion of interest, the wide range of ions for which ionophores are available, and because they can borrow from ongoing developments in ion-selective electrode technology. As is the case with ion-selective electrodes, most solid state sensors have used poly(vinylchloride) (PVC) as a membrane matrix. One of the primary causes of failure in conventional microsensors has been poor adhesion of the organic membrane to the chip surface. This leads to the formation of electrolyte shunts around the membrane, rendering the membrane inoperative.
Others in the prior art have endeavored to improve membrane adhesion such as by the use of a polyimide suspended mesh, modification of PVC for binding to hydroxyl-bearing surfaces, and mechanical attachment of the membrane. These methods have tended to improve adhesion of the membrane, but generally have resulted in either inferior electrochemical performance when compared to PVC or adding processing complexity. There is, therefore, a need for a permselective membrane which exhibits good electrochemical properties, preferably at least as good as traditional PVC membranes, but which exhibits excellent adhesion to the Si.sub.3 N.sub.4 surface of solid state sensors.
Silicone has been used for forming chemical-selective membranes. Usually, such membranes are in the form of a silicone rubber tubing which is impregnated with an ionophore. In other known arrangements, the silicone rubber is pressed into a pellet. One commercially solvent castable two-part system which is based on silicone rubber has been employed to form chemical-selective membranes. However,.the only success with this known approach has been in sensing pH. Moreover, the known approach produced a membrane which did not adhere well to surfaces.
It is, therefore, an object of this invention to provide a substance-sensitive solid state sensor which has an extended lifetime.
It is another object of this invention to provide a substance-sensitive membrane system for a solid state sensor which is possessed of excellent electrochemical properties.
It is also an object of this invention to provide a substance-sensitive membrane system for a solid state sensor which is characterized with excellent adherence to solid state sensor materials.
It is a further object of this invention to provide a substance-sensitive membrane system for a solid state sensor which can be applied to a plurality of solid state devices simultaneously using conventional integrated circuit manufacturing techniques.
It is additionally an object of this invention to provide a solid state sensor system which is not subject to the generation of disabling electrolyte shunts around the substance-sensitive membrane.
It is yet a further object of this invention to provide a solid state sensor system which is simple and low in cost.
It is also another object of this invention to provide a substance-sensitive polymeric membrane system for a solid state sensor which can be applied to a multiplicity of solid state devices simultaneously using conventional integrated circuit manufacturing techniques and which utilizes ionophoric doping to create the substance sensitivity.
It is yet an additional object of this invention to provide a substance-sensitive membrane for use with a solid state sensor and which does not require a structural layer associated therewith to maintain communication between the membrane and a solid state substrate.
It is still another object of this invention to provide a substance-sensitive solid state sensor which can be manufactured inexpensively in production quantities, and which can be adapted for industrial uses, such as monitoring treated or waste water for hardness or pollutants, on-line analysis of industrial chemicals, foodstuffs, and medicines, and low cost analytical instruments.
It is a yet further object of this invention to provide a substance-sensitive solid state sensor which can be manufactured inexpensively in production quantities, and which can be adapted for medical uses, such as monitoring of electrolytes, blood gases, and medical substrates.
It is also a further object of this invention to provide a substance-sensitive solid state sensor which can be manufactured inexpensively in production quantities, and which can be adapted for biochemical control systems.
It is additionally another object of this invention to provide a substance-sensitive solid state sensor which can be manufactured inexpensively in production quantities, and which can be adapted for patient monitoring and diagnostics.
A still further object of this invention is to provide a substance-sensitive membrane for use in a solid state sensor, wherein the membrane exhibits good adhesion to SiO.sub.2 surfaces.
An additional object of this invention is to provide a substance-sensitive membrane for use in a solid state sensor, wherein the membrane exhibits good adhesion to Si.sub.3 N.sub.4 surfaces.
Yet another object of this invention is to provide a substance-sensitive membrane for use in a solid state sensor, wherein the membrane exhibits a reduced electrical resistance characteristic and thereby yields reduced electrical noise for the sensor.
Another object of this invention is to provide a substance-sensitive membrane for use in a solid state sensor, wherein the membrane exhibits a reduced tendency to adsorb protein.
A yet further object of this invention is to provide a substance-sensitive membrane for use in a solid state sensor, wherein the membrane exhibits a reduced tendency to cause blood clotting.